摘要:

Twelve plants each of 94 collections of maize (Zea maysL. subsp.mays) representing 34 races from Mexico were analyzed for 13 enzyme systems encoded by 23 loci. This analysis revealed an exceptionally high level of variation within and among the races. We recorded an average of 7.09 alleles/locus and an expected heterozygosity of 0.182. Seventy‐two percent of the isozyme variation resided within collections, and 27% among collections. Races from northern and northwestern Mexico tend to possess higher levels of variation than those from the south. Variation for some isozyme alleles is strongly correlated with altitude. Maize is among the most variable species that have been studied isoenzymatically. Maize has levels of variation comparable to those found in its wild relatives, the teosintes. Principal component and cluster analyses showed continuous variation among the races with no well‐defined racial complexes; however, three weakly differentiated groups were apparent: 1) the high‐elevation Mexican pyramidal races, 2) the northern and northwestern races, and 3) most remaining races including the southern and western low‐elevation dent and flour corns.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1985.tb08320.x

出版商:Wiley    

年代:1985

数据来源: WILEY

摘要:

We use a model population comprised of five genotypes ofPhlox paniculataL. to investigate the contribution of individuals to the response breadth (niche) of the population on a light gradient and a moisture gradient. Analysis of within‐ and between‐genotype components of population response width showed up to 20% of the response is due to between‐genotype effects, depending upon the character considered. Since the only way a sedentary organism can deal with a variable environment is through plasticity of response, differences in levels of phenotypic plasticity between genotypes on the two resource gradients were also investigated. There was no correlation between level of phenotypic plasticity and success over a range of environments. Niche breadth calculated as Levins' (B) and Roughgarden's (w2) indicated that flowering, and hence sexual reproduction, was limited to a much narrower range of environments than was vegetative growth. We also found significant genotype × environment interactions on both gradients, indicating differences in genetic response to the environment.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1985.tb08321.x

出版商:Wiley    

年代:1985

数据来源: WILEY

摘要:

Two new species of the late Paleozoic fernScolecopteris(Marattiales) are described and their relationships within the genus are discussed.Scolecopteris charmasp.n., from Steubenville, Ohio (Duquesne Coal, Upper Pennsylvanian), is similar to species in the Oliveri group, whileS. gnomasp.n. from Providence, Kentucky (Baker Coal, Middle Pennsylvanian), compares favorably with the Latifolia species group.Scolecopteris gnomais most similar toS. fragilisbut differs in its smaller synangia and spore type.S. charmaappears generally similar toS. iowensisbecause of its large pedicel and histologically undifferentiated walls, but differs in a number of characters such as vasculature and spore type. Despite its occurrence late in the Pennsylvanian,S. charmais thought to possess a number of primitive character states (large trilete spores, vascularized pedicels, flat pinnules with downturned margins). Using the same criteria for the much olderS. gnoma, we note a number of relatively apomorphic character states (small monolete spores, unvascularized pedicels, extended pinnule margins). An outgroup analysis of species‐level characters ofScolecopterisgives a better concept of primitive versus derived traits in marattialean and other ferns. Genera in the Paleozoic fern orders Filicales (Ankyropteris) and Zygopteridales (Corynepteris,Musatea) were chosen as outgroups, and the comparisons support suggestions for the polarity of several important characters. Some of these agree with previously proposed evolutionary polarities based on the geological occurrence of marattialean ferns.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1985.tb08322.x

出版商:Wiley    

年代:1985

数据来源: WILEY

摘要:

It has been demonstrated that antheridiogens determine gametangial initiation in cultures of some homosporous fern gametophytes. Studies of natural populations have implicated these compounds as breeding system controllers. InCystopteris, response to antheridiogen varied significantly among species. WhileCystopteris protrusaresponded to exogenous antheridiogen,C. bulbiferadid not. The allopolyploid derivative of these two species,C. tennesseensis, had an intermediate level of response. This marked physiological difference among morphologically similar taxa is valuable in delineating species and suggests a mechanism that may be associated with interspecific hybridization.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1985.tb08323.x

出版商:Wiley    

年代:1985

数据来源: WILEY

摘要:

Zygotene synaptonemal complex karyotyping of five strains of diploidTradescantiawas carried out using the whole mount spreading technique. The presence of pairing partner switches in the zygotene preparations suggested the presence of chromosomal structural heterozygosity. Metaphase and Anaphase I analysis confirmed the presence of heterozygous translocations and inversions. Two plants analyzed had large centric fragments. In a nucleus from one, the fragments were completely synapsed; in a nucleus from the other, there was very little synapsis. Difficulties arose in adapting the whole mount spreading technique to the longTradescantiachromosomes. Variability was encountered in both the contrast obtained and in the degree to which the chromosomal axes were stretched. Possible sources of the variability are discussed.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1985.tb08324.x

出版商:Wiley    

年代:1985

数据来源: WILEY

摘要:

Serial peels through the branch junctions ofPsilophyton dawsoniiwere examined in an attempt to determine if “hydraulic constrictions” (i.e., a localized decrease in mean diameter of xylem elements) sensu Zimmermann (1983) had occurred during bifurcation. Based on the mean diameters of primary xylem tracheids measured acropetally and basipetally to branch junctions, evidence for xylem constrictions (= localized decrease in mean tracheid diameter) was found within the basalmost portions of four out of six minor axes examined near their attachment to major axes (anisotomous junctions). Xylem constrictions were not detected in branch junctions between axes of equal girth (isotomous junctions). Xylem constrictions were detected within the base of five out of seven junctions between fertile and main axes. The mean diameters of tracheids of the branch trace near its origin are larger both basipetally and acropetally from the constriction. There is no evidence for a localized decrease in the mean diameter of the xylem strand in the region of a constriction. Therefore, xylem constrictions are not the result of epidogenesis. Based on the production of “hydraulic constrictions” in extant plants, which serve to localize the formation of embolisms in lateral branches during water stress, it is speculated thatP. dawsoniicould protect the vasculature of major axes by a similar anatomical feature.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1985.tb08325.x

出版商:Wiley    

年代:1985

数据来源: WILEY

摘要:

To help identify possible element stresses, seedling responses ofAgave desertito high concentrations of various elements were examined by monitoring both 12‐day growth in hydroponic solution and 6‐month growth in sand culture. In addition, nocturnal acid accumulation by adult plants of six agave species was related to element levels in their chlorenchyma. Compared with common agronomic plants, seedlings ofA. desertiwere quite sensitive to salinity, with 50 mm NaCl greatly reducing root elongation in hydroponic solution and watering with 25 mm NaCl preventing growth in sand culture. The seedlings were rather insensitive to Ca concentrations from 0.2 to 5 mm and to pH from pH 5 to 8. They also tolerated high levels of B and of the heavy metals Cu and Zn. Nocturnal acid accumulation by adult plants of the six agave species was positively correlated with levels of 10 elements in the chlorenchyma, especially N (r2= 0. 70), B (r2= 0.51), and Ca (r2= 0.46). In contrast, nocturnal acid accumulation was weakly and negatively correlated with chlorenchyma Na (r2= 0.13), consistent with the deleterious effects of salinity on the growth of seedlings. Correlations between nocturnal acid accumulation and element content were consistent with previous fertilizer experiments with N, B, Ca, K, and P onA. sisalana. Element levels in the chlorenchyma of the six agave species were generally similar to those of previously studied cacti, including a low Na and high Ca level compared with agronomic plants.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1985.tb08326.x

出版商:Wiley    

年代:1985

数据来源: WILEY

摘要:

Twenty winter cultivars ofTriticum aestivumL. (wheat) were grown in solution culture with and without aluminum (Al) (74μM, 2.0 mg L‐1) for 14 days. Exposure to Al increased root growth of the most tolerant cultivar, while both root and shoot growth were depressed in all other cultivars. On the basis of a root tolerance index (RTI = weight of roots grown with Al/weight of roots grown without Al), cultivar tolerance to Al ranged 9‐fold, from 0.13 ± 0.01 to 1.16 ± 0.10. Symptoms of Al toxicity were most evident on roots. Aluminum‐affected roots were relatively short and thick and had numerous undeveloped laterals. Leaves of some cultivars showed chlorosis resembling iron deficiency, and others showed purple stems typical of phosphate deficiency.Plants of all cultivars grown with and without Al depressed the pH of nutrient solutions, presumably until NH4+was depleted, at which point the pH increased. Cultivar tolerance, expressed both as the root tolerance index and a shoot tolerance index, was negatively correlated with the negative log of the mean hydrogen ion (H+) concentration, the minimum pH, and the slope of the pH decline, each calculated from pH data collected during the first 9 days of the experimental period before any sharp rises in pH occurred. These results are consistent with the hypothesis that the Al tolerance of a given cultivar is a function of its ability to resist acidification of the nutrient solution and hence to limit the solubility and toxicity of Al.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1985.tb08327.x

出版商:Wiley    

年代:1985

数据来源: WILEY

摘要:

Twenty spring cultivars ofTriticum aestivumL. (wheat) were grown in solution culture with and without aluminum (Al) (74μM, 2.0 mg L‐1) for 14 days. Root growth and shoot growth were depressed in all cultivars grown with Al; however, symptoms of Al toxicity were most evident on roots. Based on a root tolerance index (RTI = weight of roots grown with Al/weight of roots grown without Al), cultivar tolerance ranged from 0.18 ± 0.02 to 0.85 ± 0.03. Aluminum‐affected roots were relatively short, thick, and had numerous undeveloped laterals. Leaves of some cultivars showed chlorosis resembling iron deficiency and others showed purple stems typical of phosphate deficiency.Plants of all cultivars induced a progressive decline in nutrient solution pH from the outset of the experiment until Days 10–14. After this initial period, some cultivars rapidly increased solution pH, while others continued to depress solution pH throughout the experiment. Cultivar tolerance expressed as the RTI was negatively correlated with the negative log of the mean hydrogen ion (H+) concentration, the minimum pH, and the slope of the pH decline, each calculated from pH data collected during the first 9 days of the experimental period before any sharp rises in pH. The relationship between solution pH and Al tolerance was similar to that reported previously for winter cultivars ofT. aestivum, suggesting that the Al tolerance of a given cultivar is a function of its ability to resist acidification of the nutrient solution and hence to limit the solubility and toxicity of Al.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1985.tb08328.x

出版商:Wiley    

年代:1985

数据来源: WILEY

摘要:

Severe chlorosis and ultrastructural modifications of chloroplasts occur in sunflower in response to infection byPseudomonas syringaepv.tagetis. Chlorosis became apparent within 2 days after the cotyledons of 10‐day‐old sunflower seedlings were inoculated with the bacteria. The first symptoms generally appeared in the center of leaves at the second node above the cotyledons. Leaves above the second node lost essentially all of their pigmentation but remained turgid and continued to expand. Grana thylakoids became dilated and separated from the granal stacks. These thylakoid membranes did not chemically breakdown as in the case in chromoplast formation or normal chloroplast senescence. Both grana and stroma thylakoid membranes coalesced to form a large membrane sheet within the plastid. The ultrastructural changes are unlike those reported to be caused by other chlorosis‐inducing bacteria or chlorosis associated with normal senescence.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1985.tb08329.x

出版商:Wiley    

年代:1985

数据来源: WILEY